This invention relates to an apparatus for the U-shaped application of an adhesive tape in longitudinal direction about a flat shaped part, in particular a shaped sheet metal part, having a tape guidance which comprises conveying rollers and means for pre-folding the adhesive tape, from which means the pre-folded tape passes between two application rollers being urged against one another, by means of which rollers it can be pressed simultaneously on to the two sides of the shaped flat part being introduced into the tape-folding range.
The gluing over of folded seam connections by means of pressure- or heat-hardenable ahhesives is widely used in the sheet-metal processing industry. Thus, it is for instance conventional in the automobile industry to seal, in this manner, folded seams in certain automobile body parts, in particular doors, thereby preventing the danger of corrosion.
In the automobile industry and similar branches of industry, it is common to use adhesives in liquid or pasty form, for producing such glued-over folded seam connections, which are applied in the shape of a chord on to the metal sheet parts to be connected. This method of applying the adhesive is unsatisfactory in various respects. Firstly, the distribution of the adhesives obtained thereby over the entire folded seam is not sufficiently uniform, which may lead to problems of corrosion, and, on the other hand, adhesives in liquid or pasty form always are problematic in view of aspects of work hygiene. In the manufacture of preservative cans it is also conventional, as shown in U.S. Pat. No. 3,125,056, French Pat. No. 2,252,147 or respectively, Belgian Pat. No. 444,014, to glue over folded seams or seal them by means of adhesive. In doing so, the adhesive is deposited on the crimped rims of the parts to be connected with each other, either in liquid or in pasty form by extrusion or the like, or, otherwise, in the form of a strip of an adhesive foil.
Adhesives in film-, in particular in tape-shape, such as are known, for instance, under the trade names of Araldit-Klebfilm.RTM. and Redux-Klebfilm.RTM. manufactured by Ciba-Geigy AG, Basel, Switzerland, are more and more widely used, not at the least, because of their advantages in work hygiene. However, in the gluing over of folded seams, for instance, of automobile body parts, such tapes were not used up to now, or were only used to a very limited extent. The reason for this lies above all in the fact that adhesive films are of tough plasticity, and their very low tensile strength considerably encumbers their automatic application. Additional complications occur, when such adhesive strips must be applied to automobile body parts whose folded seams have a complicated, especially a spatially curved configuration. These difficulties are particularly great when the adhesive is to be applied on both sides to the crimped rim, i.e., when the adhesive tape must be placed on to the rim in the shape of a U.
Most of the hitherto known apparatus of the type initially described are only suitable for processing relatively stiff adhesive ribbons (not adhesive tapes) of relatively high tensile strength. This is true, for instance, in the case of the apparatus having a pre-folding channel and pressure pulleys, known from the U.S. Pat. No. 4,155,798.
In recognition of the fact that the failure of the known apparatus to be suitable for the application of tough plastic adhesive tapes of low inherent stiffness and tensile strength on to curved sheet metal rims is, above all, due to the rigid arrangement of the pre-folding channel and of the pressure and application rollers and also by the application rollers being freely rotating (U.S. Pat. No. 4,155,798), an arrangement has also been proposed (European Pat. No. 72,779) in which, firstly, the application roller pair is pivotable as a unit about an axis which extends parallel with the roller shafts and, with regard to the direction of transportation of the tape, spaced from the latter, approximately in the plane of symmetry of the pre-folding channel, and in which, secondly, the application rollers are drivable by a motor via torsion-elastic shafts. This device does indeed represent a jump in improvement over the known state of the art; however, detailed tests in practice have shown that, with regard to the quality of application in particular at higher application speeds, there is still room for decisive improvement of the same.